Upscaling hydrogen-enriched methane MILD combustion furnaces: A numerical investigation and thermal analysis

In pursuit of decarbonisation goals, hydrogen-enriched methane under MILD (Moderate or Intense Low-oxygen Dilution) combustion is a promising technology that reduces NO x emissions and improves furnace combustion efficiency. This study numerically investigates scaling up MILD laboratory furnaces from 10 kW to 200 kW and ultimately to an industrial scale of 1 MW. To improve the prediction of steady-state simulations, the extended eddy dissipation concept for turbulence-chemistry interaction and a weighted-sum-of-gray-gases model adapted for hydrogen-methane mixtures were implemented and validated for MILD combustion. A 50%–50% hydrogen-methane volumetric blend was considered, as this composition enables a stable MILD regime in the baseline configuration. A scaling-based approach grounded in established criteria from the literature was employed, evaluating the constant residence time criterion and the constant jet momentum to volume criterion. Temperature fields, MILD regime stability, heat transfer, and emissions were analysed across laboratory-scale and scaled-up furnaces. The constant residence time criterion, with adequately scaled wall thermal resistance, effectively preserved the MILD regime by maintaining the Damköhler number, but its associated pressure drop becomes impractical for industrial applications. Although the constant jet momentum criterion substantially reduces this pressure drop, it was found to slightly destabilise the MILD regime, requiring the definition of appropriate heat extraction operating conditions. Scaling criteria alone were insufficient to guarantee MILD regime stability. Integrating heat transfer analysis of the refractory lining and defining load-dependent operating limits proved essential, particularly with hydrogen-enriched fuels. Following this approach, the furnace was successfully scaled to 1 MW, supporting the industrial deployment of MILD combustion for decarbonisation. • Conventional scaling criteria provide a solid framework for transferring MILD burner designs to larger scales. • Scaling laws alone are insufficient: thermal analysis of the refractory lining must be incorporated. • Load-dependent operating limits must be defined to sustain the MILD regime at every scale. • The CM criterion offers a practical alternative to the CRT criterion, with significantly lower pressure drop at industrial scale. • MILD combustion with hydrogen-methane blends has been successfully scaled from laboratory scale to 1 MW.